A common steel reinforced concrete building or structure form is a horizontal flat slab or plate supported by vertical columns or beams and the like. Because of the transfer of shearing forces and moments, such structures can be subject to brittle punching failures which are manifested by cracks extending as an inverted cone or pyramid through the slab, beam, or plate at the supporting column or beam. The cracks extend at their lower end from the tensile area of the slab or beam to the compressive area or top.
Adequate strength, drift capacity and ductile behavior can be obtained by increasing the slab thickness in the area of the column or beam or providing the column with a shear capital or enlargement at the top. These solutions, however, are costly and space consuming. A more cost effective approach is to provide the horizontal element around the column or at the beam with shear studs or stirrups. Shear studs are relatively short rods which have an upset or enlarged head at one or both ends. The use of separate or individual shear studs is rare because they can be loose during the pour and the heads or ends have to be spaced from the top and bottom of the slab. If supported from a bottom form for the slab, a chair is usually required.
Present practice consists of single or double headed studs connected at one end by a steel strip, rail or rod to hold and position the studs as an assembly for positioning in the slab formwork around a column. The rail or rod is connected along the top or bottom of the studs and most commonly by shop fabrication welding. Examples may be seen in U.S. Pat. Nos. 4,406,103 and 4,612,747. Thus, the shear reinforcement assemblies are part of the steel reinforcing design and such are delivered to the job site already assembled or fabricated. The assembly may be quite heavy, bulky, and unwieldy. One of the major problems with the use of such factory formed shear stud assemblies is that they will not fit the area of intended insertion because such area is already heavily congested with steel reinforcing. In the design of steel reinforcing tolerances are measured in centimeters (cm), and though the shear stud assembly may fit on the drawing board or in the computer graphics, it simply will not go where it is supposed to go, at least without considerable banging or reworking of the steel reinforcement, or refabrication. Sending it back to the shop with a pour already scheduled is usually out of the question. The difference between installation drawings and field conditions and practice is often significant. The force fit of prefabricated assemblies often produces results less optimal than as originally designed.